This invention relates to an industrial robot which can automatically correct the "deviations" of a large number of teaching points so as to perform accurate tasks.
For example, in a case where workpieces arrayed on a conveyor are subjected to predetermined spot welding tasks by an industrial robot, an expedient is employed in which, before the tasks, the plurality of workpieces are actually arrayed on the conveyor and the positions thereof are taught to the robot. On account of an inferior job environment, however, it is unfavorable for safety that such a teaching operation is conducted in a production line.
As an expedient for coping with this drawback, there is a method wherein using, for example, a programming device installed in a safe place remote from a production line, such as a design room, information items such as "the position of a conveyor", "the positions of workpieces", "the shapes of workpieces", "the position of a robot", and "teaching points"are input to teach the motion of the robot in an off-line fashion, and these overall information items are loaded in the robot so as to cause the robot to perform predetermined tasks.
Since, however, the aforementioned off-line "position of the conveyor", "positions of the workpieces", "position of the robot" etc. inevitably involve errors relative to actual positions, the teaching points for the respective workpieces on the conveyor deviate. This leads to the disadvantage that the spot welding, for example, cannot be performed for the workpieces.
As another example, a workpiece is successively moved to a plurality of machine tools or workbenches by a single industrial robot. In such a case, a large number of teaching points must be set on the machine tools or workbenches before the tasks. However, the relative positions (positions in directions X, Y and Z) of the individual machine tools or workbenches often deviate relative to preset positions. Therefore, when the aforementioned series of tasks are taught in off-line fashion under such a state and the corresponding information is loaded in the robot, it is inevitably impossible to carry out the normal tasks. Accordingly, the "deviations" of the teaching points need to be corrected.
However, even when the "deviations" of the teaching points have been corrected for one of the machine tools or workbenches, the teaching points for this machine tool or workbench deviate because the other machine tools or workbenches are not installed on their preset positions. After all, the series of tasks are impossible.